The present invention relates to apparatus and methods for concentrating a looked-for element from a solution for flameless atomic absorption spectroscopy, wherein the looked-for element is deposited on a carrier by electrolysis, and the carrier, with the electrodeposition, is heated in the path of rays of an atomic absorption spectrometer to atomize the deposited components.
In flameless atomic absorption spectroscopy, a metered portion of a sample is disposed in a graphite tube. The graphite tube is radiated in a longitudinal direction by the measuring beam of an atomic absorption spectrometer. The measuring beam consists of light having the resonance wavelength of the looked-for element. The graphite tube is heated to a high temperature by electric current. The sample is thus decomposed and vaporized (atomized), whereby the elements of the sample are present in the graphite tube in their atomic states in a "cloud of atoms". The measuring beam, which, as mentioned above, consists of light having the resonance wavelength of the looked-for element, is absorbed in accordance with the quantity of the looked-for element in the sample, as each element in its atomic state absorbs its resonance wavelength only.
This measurement can be disturbed by smoke, which forms when the sample is vaporized, and which results in absorption of the measuring beam. If the smoke develops at the same temperature at which the looked-for element vaporizes, measurement may sometimes become impossible.
To avoid these problems, it is known to deposit the looked-for element by electrolysis from a sample solution in a graphite crucible (Annali di Chimica, 67 (1977), pages 557 to 566). In this method, a crucible of glassy carbon is used, and is supported between two graphite rods below the path of the rays of the measuring beam of an atomic absorption spectrometer. A circulation system with two coaxial small connecting sockets opens into the graphite crucible. In this manner a sample is pumped into and suctioned from the crucible. During its flow through the crucible, the sample solution is subjected to electrolysis, the crucible constituting one electrode for the electrolysis on which, for example, metals are deposited.
Subsequently, a washing solution is flushed through the crucible, and the circulation system is removed. The crucible is then heated by an electric current, whereby the deposited electrodeposition is vaporized and displaced into the path of rays of the atomic absorption spectrometer as a cloud of atoms.
The above described method requires a relatively expensive apparatus and, because of the necessity of circulating the sample solution, requires a relatively large sample quantity. The whole procedure takes place within the atomic absorption spectrometer. The cloud of atoms forms in free space above the crucible and is therefore dissipated very quickly due to diffusion. This method would not be applicable with a graphite tube.